Efficacy of 1-a-Hydroxycholecalciferol supplementation in young broiler feed suggests reducing calcium levels at grower phase

Authors: WARREN, MATTHEW - North Carolina State University; Vu, Thien; Toomer, Ondulla; FERNANDEZ, JUAN - Premex; LIVINGSTON, KIMBERLY - Elanco Animal Health, Inc

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2020
Publication Date: 6/10/2020
Citation: Warren, M.F., Vu, T.C., Toomer, O.T., Fernandez, J.D., Livingston, K.A. 2020. Efficacy of 1-a-Hydroxycholecalciferol supplementation in young broiler feed suggests reducing calcium levels at grower phase. Frontiers in Veterinary Science. 7:245. https://doi.org/10.3389/fvets.2020.00245.
DOI: https://doi.org/10.3389/fvets.2020.00245

Interpretive Summary: This manuscript titled 'Efficacy of 1-a-Hydroxycholecalciferol supplementation in young broiler feed suggests reducing calcium levels at grower phase' examines how the synthetic vitamin D3 form, 1-a-Hydroxycholecalciferol (1a) affected broiler diets when supplemented in starter and grower phase with increasing levels of calcium inclusion. Exploring means to improve biopotency of dietary vitamin D will be valuable for the poultry industry to meet nutritional demands of fast-growing broilers. 1a has similar efficacy to the active form of vitamin D3 (1,25-dihydroxycholecalciferol), but is cheaper to synthesize and supply in diets. This work examined how 1a and calcium inclusion influenced ionized blood calcium, plasma vitamin D metabolites, and gene expression of intestinal genes related to tight junction or mineral transport. We found that chicks fed 1a during starter phase had a linear increase in ionized blood calcium as calcium inclusion increased. We also observed with grower phase, broilers fed 1a had a decrease in plasma 25-hydroxycholecalciferol concentration as calcium inclusion increased. Our findings also indicate that while 1a is effective with starter phase of broiler diets, there may be potential complications with 1a supplementation in grower phase because of calcium toxicity or antagonism so reducing dietary calcium may be necessary.

Technical Abstract: Increasing biopotency of cholecalciferol (D3) from vitamin sources is essential in the poultry industry to meet nutritional demands and counter stressors. D3 exhibits hormonal traits and is responsible for calcium (Ca) absorption. 1-a-Hydroxycholecalciferol (1a) is a synthetic form of D3 that has equal efficacy and is cheaper to synthesize than 1,25-dihydroxycholecalciferol (active form of D3), on broilers. However, 1a bypasses a critical regulatory point, the kidney, and may consequently lead to toxicity levels of Ca via Ca absorption. This study examined 1a supplementation in broiler diets with different Ca inclusion levels to determine if 1a at higher Ca levels caused Ca toxicity at starter and grower phases with Ross 708 male broiler chicks. In Experiment 1 (1–15 days of age), chicks were assigned to one of 10 treatment starter diets with five levels of Ca inclusion (0.80, 0.95, 1.10, 1.25, and 1.40%) with or without 1a supplementation (5 µg 1a/kg in feed) and eight replicate cages per treatment. In Experiment 2, chicks were fed common starter diet until 16 days of age, and then they were assigned to one of eight treatment diets with four levels of Ca inclusion (0.54, 0.76, 0.98, or 1.20%) with or without 1a supplementation (5 µg 1a/kg in feed). At the end of both experiments, blood was collected from broilers to determine blood chemistry, including concentrations of vitamin D metabolites. Intestinal tissues were also collected to examine gene expression. In Experiment 1, broilers not fed 1a exhibited a quadratic effect in ionized blood Ca (iCa) as dietary Ca inclusion levels increased; 1a-fed broilers displayed an increase in iCa as Ca inclusion levels increased (p = 0.0002). For Experiment 2, 1a-fed broilers displayed a decrease in 25-hydroxycholecalciferol plasma concentration as dietary Ca inclusion levels increased (p = 0.035); also, increasing Ca inclusion in diets increased expression of duodenal sodium phosphate cotransporter type II b (NPTIIb, p = 0.03). Our findings imply that inclusion of 1a was beneficial because 1a enhanced Ca absorption during the starter phase; however, to avoid potential Ca toxicity or antagonism while using 1a during the grower phase, there should be consideration with reducing dietary Ca levels.